1. Field of the Invention
This invention relates to improvements in tube expanders of the roller and mandrel type which utilize a stop collar to restrain axial displacements of the tube to be expanded.
2. Description of the Prior Art
Various types of tube expanders of the roller and mandrel type for expanding tubes in tube sheets are known. In expanding thin-walled tubes having a wall thickness of approximately 22 gauge or thinner in tube sheets, it has been common to employ an expander which includes a tubular cage with slots containing rollers lying at an oblique angle to the axis of the cage and a tapered mandrel extending through the cage and movable into and out of contact with the rollers. When such an expander is inserted into a tube and the mandrel is advanced and rotated so as to force the rollers into contact with the tube, the movement of the mandrel causes the cage to rotate with the mandrel and to move into the tube. This movement of the cage continues until arrested by engagement with the tube sheet of a collar mounted on the cage to rotate therewith. The collar will generally have an internal radial shoulder opposed to the end of the tube for engagement therewith. During further rotation of the cage to complete the expansion of the tube, while movement of the cage into the tube is prevented, the rollers act to pull the tube outward from the sheet and into contact with the shoulder in the collar.
Under such arrangements, continued rotation of the cage will cause the rotating housing collar to mar the outer surface of the tube sheet around the end of the tube and to deform, curl or otherwise damage the end of the tube. Often the housing collar is unable to restrain thin-walled tubes since the outwardly directed forces are great enough to shear off the edge of the tube or suck the tube underneath the collar.
The difficulties are peculiarly applicable to thinwalled tubes in which the wall thickness of the tube after expansion is sufficiently thin to provide an extremely small contact area for use in offsetting the comparatively substantial traction forces tending to pull the tube out of the tube sheet. For example, in expansion of a tube of 22 gauge wall thickness, the outer diameter (O.D.) of the tube being approximately 0.875 inches, the actual dimension of the wall is approximately 0.028 inches, leaving a nominal inner diameter (I.D.) of approximately 0.819 inches. Assuming that the tube sheet opening is 0.890 inches, the tube must be expanded to 0.834 inches I.D. to achieve metal-to-metal contact, thus leaving approximately 0.020 inches of material on each side of the collar with which to bear against to offset the outward traction forces of the expansion rollers of the tube expander. In practice, it has been found that the magnitude of the traction forces, in comparison to the amount of tube material available to offset these forces, often causes the collar to be ineffective, with the result that the tube is sucked underneath the collar and totally destroyed.
Some attempts have been made in the past to provide the necessary anti-traction axial support forces while maintaining the desired axial dimension between the tube and tube sheet and avoiding marring or damaging forces to which the tube sheet and the tube would otherwise be subjected. In my U.S. Pat. No. 3,426,565 there is disclosed a tube expander of the roller and mandrel type which includes a relatively large and resilient thrust ring surrounding the expansion rollers while remaining in close contact with an end portion of a tube. The portion of the thrust ring which contacts the end portion of the tube exceeds the wall thickness of the tube end. As a result, the thrust ring distributes the axial load thereon without damaging the tube. Also, the thrust ring restrains axial displacement of the tube from the tube sheet. Although the thrust ring of my '565 patent has been found to be quite successful, it nevertheless has been found to be expensive to manufacture. In addition variations of the axial positioning of the end of the tube relative to the tube sheet are only accomplished by having available, thrust rings of various constructional dimensions, each corresponding to a predetermined amount of exposure which may be desired between the tube and tube sheet.
U.S. Pat. No. 3,924,433 to Martin relates to a tube expander of the roller and mandrel type, wherein a thrust collar limits outward advancement of a tube end which is received in a tube sheet. This thrust collar has a plurality of independently movable L-shaped wire fingers which contact the tube end. In use, these fingers develop relatively large stress localizations at the end of the tube, which stress localizations have been found to cause severe distortions to the end of the tube, particularly when the tube has a thin wall. In addition, the dimensions of the L-shaped wire fingers are fixed, thus fixing for any given collar, the dimension between the end of the tube and the tube sheet.
While these patents represent improvements in tube expanders of the type contemplated, they do not disclose expanders capable of readily limiting the axial position of an expanded tube within a tube sheet according to predetermined and readily selectable tube positions without causing damage to the end of the tube. I have invented a tube expander which not only accomplishes these ends, but provides an infinite number of positions for the tube relative to the tube sheet by a relatively simple and inexpensive arrangement.